1. Field of the Invention
The present invention relates generally to battery powered devices and, more particularly, to the identification of the chemistry of a battery pack installed in such devices.
2. Related Art
Sudden cardiac arrest, i.e., a heart attack, has been attributed to over 350,000 deaths each year in the United States, making it one of the country's leading medical emergencies. World-wide, sudden cardiac arrest has been attributed to a much larger number of deaths each year. One of the most common, and life threatening, consequences of a heart attack is the development a cardiac arrhythmia commonly referred to as ventricular fibrillation. When in ventricular fibrillation the heart muscle is unable to pump an sufficient volume of blood to the body and, more importantly, to the brain. Ventricular fibrillation is generally identifiable by the victim's immediate loss of pulse, loss of consciousness and a cessation of breathing. The lack of blood and oxygen to the brain may result in brain damage, paralysis or death to the victim.
The probability of surviving a heart attack or other serious heart arrhythmia depends on the speed with which effective medical treatment is provided. There are four critical components of effective medical treatment that must be administered to a victim of sudden cardiac arrest: (1) early cardiopulmonary resuscitation to keep the blood oxygenated and flowing to the victim's brain and other vital organs; (2) early access to emergency care; (3) early cardiac defibrillation to restore the heart's regular rhythm; and (4) early access to advanced medical care. If prompt cardiopulmonary resuscitation is followed by defibrillation within approximately four minutes of the onset of symptoms, the victim's chances of surviving sudden cardiac arrest can approach or exceed forty percent. Prompt administration of defibrillation within the first critical minutes is considered one of the most important components of emergency medical treatment for preventing death from sudden cardiac arrest.
Cardiac defibrillation is an electric shock that is used to arrest the chaotic cardiac contractions that occur during ventricular fibrillation and to restore a normal cardiac rhythm. To administer this electrical shock to the heart, defibrillator pads are placed on the victim's chest, and an electrical impulse of the proper size and shape is administered to the victim in the form of an electric shock. While defibrillators have been known for years, they have typically been large and expensive making them unsuitable for use outside of a hospital or medical facility.
More recently however, portable external defibrillators for use by first responders have been developed. A portable defibrillator allows proper medical care to be given to a victim earlier than preceding defibrillators, increasing the likelihood of survival. Such portable defibrillators may be brought to or stored in an accessible location at a business, home, aircraft or the like, ready for use by first responders. With recent advances in technology, even a minimally trained individual can operate conventional portable defibrillators to aid a heart attack victim in the critical first few minutes subsequent to onset of sudden cardiac arrest.
Portable defibrillators require an energy source other than alternating current to operate in the anticipated mobile environment. Several manufacturers have provided customized battery packs for their defibrillators. More commonly, however, portable defibrillators use a standard, commonly available, rechargeable battery pack, such as those used in video camcorders. Such battery packs are generally referred to herein as industry standard battery packs. The use of industry standard battery packs allows for the easy and inexpensive purchase of replacement batteries when needed. These battery packs, while often having a standard mechanical and electrical interface, are available with different chemistries, such as lead acid, nickel cadmium (NiCd), lithium or the like.
The type of battery pack installed in a particular device depends on the anticipated operating environment in which the device is to be used. The manner in which the device is operated is commonly referred to as the "use model" of the device. Oftentimes, a battery-powered device may operate in accordance with one or more use models. In the context of battery packs, use models are defined primarily by the charge and discharge characteristics imposed on the battery pack by the device. For example, a primary factor in the performance of a battery pack is the amount of discharge experienced by the battery pack in prior uses of the device. The degree of discharge may range from a deep discharge where the energy of the battery pack is substantially depleted, to shallow discharge where an insignificant amount of energy has been depleted.
Certain battery chemistries are more suitable for certain use models than others. For instance, sealed lead acid (SLA) battery packs are ideal for supporting devices which are operated for short periods of time, each operation causing a shallow discharge of the battery pack. NiCd batteries are best suited for use in devices that are used frequently with each use being for a relatively long period of time, causing the battery pack to experience a deep discharge prior to being recharged. On the other hand, lithium (Li) battery packs are best suited for use in products that are used infrequently since they can maintain a charge for a relatively long period of time and are generally not rechargeable.
Certain battery-powered devices have a specific customer and a single use model. As a result, such devices are typically designed to operate with a single battery chemistry appropriate for that use model. Oftentimes, such devices use an industry standard battery pack.
In contrast, other devices have a variety of anticipated customers and use models. Oftentimes, such devices use a custom battery pack designed to be used specifically for the particular device. The custom battery pack is available in multiple chemistries which may be selected for the anticipated use model. For example, the LifePak 500 available from Physio-Control Corporation, Redmond, Wash., has a custom battery pack capable of being loaded with either lead acid or lithium battery cells. The battery pack having the battery chemistry appropriate to support the anticipate use model is selected and used. A drawback to this approach, however, is that the custom battery packs are expensive and not readily available.
What is needed, therefore, is a system and method to cost-effectively power portable devices that operate in accordance with more than one use model.